Probes for the invasive measurement of blood parameters consist--in one embodiment--of at least one sensor comprising an optical fiber, wherein said fiber ends up with a gel zone containing a dye. The optical density or another optical parameter of the dye varies with the blood parameter (such as pH, pO.sub.2 or pCO.sub.2) to be measured. On the other side of the dye-containing gel, a reflector is positioned. The end of the fiber, the gel and the reflector are surrounded by a semi-permeable envelope (for example, a hydrogen ion permeable envelope in the case of a pH sensor) to keep the gel in place.
Light from this optical fiber passes the dye-containing gel, is reflected by said reflector, passes the gel again and is transmitted through the optical fiber to an appropriate detector which measures light attenuation or changes in other optical parameters caused by the dye. This attenuation or change is a function of the blood parameter to be measured, and the relation between attenuation, absorbance or the change of another optical parameter and the blood parameter is well-known.
Such a probe can be introduced into the patient's artery to measure--depending on the dye and/or the selected semi-permeable envelope--various blood parameters such as pH, pO.sub.2 or pCO.sub.2.
For further details of invasive blood parameter monitoring, reference is made to several patent documents which describe this technology in detail, for example, EP-A-279 004, U.S. Pat. No. 4,900,381, EP-A-336 986, EP-A-336 984, EP-A-336 985, EP-A-53 599 and EP-A-471 861, all of which are hereby incorporated by reference herein.
Such an optical probe is designed for introduction into a blood vessel of a patient. Introduction is usually performed by advancing the probe through a catheter.
It will be understood that it is a major requirement in such an application that the portion of the probe intended for blood contact is kept sterile. That is, the probe tip and other parts of the probe establishing direct blood contact may not be handled with the fingers, nor come into contact with any other non-sterile components or parts of the body. If such happens, the probe is not further useful for any medical application. Most commonly, it will be thrown away.
It is, of course, possible to keep the probe in a sterile container. However, the major problem occurs when the probe is introduced into the catheter. As soon as the sterile packaging of the probe is removed, it has to be introduced into the distal opening of the catheter (which has a very small diameter).
It will be understood that this complicated handling process may give a rise to faults. In particular, an inaccuracy upon introduction of the probe may cause physical contact between the sterile part of the probe and other non-sterile equipment, such as an extracorpular part of the catheter, a table, a part of the human body (such as the fingers of the assembling person), and the like.
Further inconveniences are caused by the fact that both the probe and the catheter may only be touched at non-sterile portions, or at their packaging. Imagine, for example, a probe and a catheter, both contained in sterile plastic bags. The assembling person may well be able to remove part of the catheter's plastic bag, and to hold the catheter at the portion still surrounded by the packaging. However, the problem now arises how to remove part of the probe's plastic bag with one hand--the other hand still holds the catheter, which may not be put down, in order to keep it sterile. One can, of course, try to hold the partially opened catheter between, let us say, the middle finger and the ring finger of the left hand, and try to open the probe's plastic bag with the thumb and the forefinger of the same hand (while the right hand holds the plastic bag of the probe). However, it is apparent that this is no perfect solution, and that the sterile part of the catheter may easily come into contact with non-sterile things or bodies.
Thus, the probe cannot be reliably introduced into the catheter by a single person, and this method is actually seldom used in clinical practice. Instead, two persons helping each other during assembly will be required (wherein one persons handles the non-sterile parts, and the other person, wearing sterile gloves, handles the sterile components, for example, on a sterile cloth).
Another problem of the method discussed above is that complicated packaging technology is required, e.g., plastic bags for all (movable) sterile components. It should also be noted that such plastic bags imply additional risk for the patient, as the plastic bag may accidentally be damaged. If such accidental damage is not observed by medical personnel, non-sterile parts come into contact with the patient's blood.
Yet another problem is that hermetic sealing between the probe and the catheter is not easy. It is evident that such sealing is required to keep the probe, as well as the interior of the catheter, in a sterile condition.
A further problem encountered is that the probe has to be recalibrated from time to time, and that the catheter has to be flushed, in order to avoid clot formation.